A murderer who slashed a woman's throat while her daughter was in the house will wait an additional two years before he is considered for parole.

The Court of Appeal, acting on an appeal by the Crown, has increased Paul Andrew Gottermeyer's non-parole period from 10 to 12 years. The court's decision, released today, found the 10-year non-parole period, imposed by Justice John Fogarty in October, was ''manifestly inadequate''.

Gottermeyer had already been sentenced to life imprisonment. The Crown asked for 13 to 14 years' non-parole based on premeditation and the victim's vulnerability, the decision said.

Mitigating factors included Gottermeyer's guilty plea, remorse, absence of any previous criminal convictions and his mental health issues, it said.

The 24-year-old victim was at her Burwood flat with her three-year-old daughter when Gottermeyer, a 30-year-old market gardener from Kaiapoi, arrived on July 11, 2012.

Gottermeyer was under treatment for depression. He had been discharged from Hillmorton Hospital, but did not continue taking his medication.

He and the woman argued before he produced a knife and began the attack in the kitchen.

The victim's body showed evidence of 12 wounds to her head, throat, chest, back and hands.

Afterwards, Gottermeyer hugged the girl and left her a glass of water, a mandarin and some biscuits in the lounge. He shut the door to the kitchen so she could not go in and see her dead mother. The woman's body was found when her partner came home later that morning to check why she had not arrived at work. He found the girl crying and upset.

Gottermeyer pleaded guilty to murder.

The Crown called the killing "callous and cruel". Justice Fogarty said at the October sentencing that he realised imposing a 10-year-old non parole period was ''not going to be popular''.

He was right.

Family of the victim, who has name suppression, reacted by shouting abuse and swearing from the court's public gallery. One yelled, "It's an injustice''.